Apparatus for electric heating devices.



F. BGLLING. APPARATUS FOR ELECTRIC HEATING DEVIGES. APPLICATION I'ILED NOV. 5, 1908.

Patented Apr. 6, 1909.

WITNESSES: INVENTOR K a/wc lmbzu BMW platesand cannot be damaged mechanically.

UNITED STATES PATENT cur os.

FRIEDRICH BOLLING, OF FRANKFORT-ON-THE-MAIN, GERMANY,

PROMETHEUS ELECTRIC 00., OF NEW YORK.

YORK.

ASSIGNOR TO THE Y., A CORPORATION OF NEW APPARATUS FOR ELECTRIC HEATING DEVICES.

Specification of Letters Patent.

Patented April 6,1909.

Application filed November 5, 1908. Serial No. tGLMG.

T 0 all whom it may concern:

Be it known that I, FRIEDRICH BoLLmG, a 1

of Germany, residing Bockenhenn, 1

useful Apparatus for Electric Heating Devices, of which tion.

The present invention has reference to resistances other purposes, resistances of United States Patent No. 617,375 to and Haellner, wherein resistances comprising thin strips of fine metal are painted on an in" sulating su port, and then fired.

Mica has een mostly used recently for the insulating sup ort. These resistances are further prefera )ly provided with a protecting mica insulating strip and are folded into sheet metal, so that the strip of fine metal FOl,lI1 two kinds of resistances are used, first; such resistances, which radiate heat freely, e. g. for stoves, and secondly; such resistances which are pressed upon a support capable of absorbing heat. The former can be loaded with about 1.5 to 2 watts per s uare centimeter, whereas with the latter a oad up tol2 watts or square centimeter isadmissible, provided that care is always taken that sufficient heat is consumed. The pressing of the resistances against the heat absorbing support is effected by pressure screws. Between the pressure plates and the heat radiating element a layer of asbestos is interposed, to prevent the heat from being too strongly conducted to the pressure plates and to obtain a uniform distribution of the pressure against the support. The load capacity of these resistance elements further depends on the condition of the body intended to absorb the heat. If the surface is plane and made exactly true, and also the pressure plate, which must be pressed against the support by means of as many screws as possible, the load capacity is very large, in any case it is double that of the general type shown in Voightstance,

' other plates which are not plane and which the heat furnishing body, a

for heating and cooking devices and E with particular reference to the following is a specificabeing inter osed, after which the pressure plate is sol ered to the heat furnishing body. This method is used with cooking vessels, since the temperature of the heat absorbing body does not run so high, that the pressure plate will melt oil.

In using the so-called open, t. 6. free radiating, elements, for stoves, a disadvantage lies in the fact that on account of the small. load capacity comparatively many elements are required to do a certain amount of work, whereby a correspondingly larger construction becomes necessary for the stove. Moreover, in the use of elements which are pressed onto the heat absorbing support, the cost of manufacturing and selling becomes very great on account of the cumbersome, time consuming and, consequently, expensive manipulations referred to. In order to avoid said disadvantages in the use of the elements known heretofore, the present invention provides for the pressing by means avoiding the use of screws or soldering and a resistance is made, which contains in itself the pressing. The well-known heating element, after the insertion of a filler-sheet of metal into the fold of the sheet metal surrounding the resistance, is laid into two sheet metal strips, closely embracing the heating element nearly for its entire length and width and made conveniently of iron sheet metal having a thickness of 1 to 1% mm. The element thus made up is pressed by means of a suitable press and with the use of a sulficiently high pressure of 350 to 500 kg. per square centimeter, in such a manner, that the two sheet metal stri )S are firmly pressed against the element inclosed within them, and are combined with it, to form a single body. By using the filler sheet metal and the sheet metal strips closely surrounding the elements, the radiating capacity oi' the elements is essentially increased and thereby also the load capacity of the heating body. An clement pressed in such a mannor, of a size of, for instance, 150x30 mm. can be loaded with 100 watts, instead of 50, without the element resting on a heat absorbing surface. Such an element can freely radiate the heat into the air. Moreover, by subjecting the element to the pressure of a press, or the like, a perfectly uniform pressing and, consequently, a smooth uniform bearing of the elements at all places heat of the heat resistance through the mica becomes very intensive. A further considerable advantage of the element made according to the present invention is this, that it can, without the requirement of a pressure plate, be easily and closely connected, by a few screws or by solder, with the surface to be heated. The time-consuming and expensive mani ulations used heretofore in pressing the e ement against the heat absorbing surface become unneccessary. The cost of manufacturing, and the sales-price, of cooking and heating devices are also essentially reduced. A further reduction in cost is effected on account of the increased load capacity of the heating elements as for a heating or cooking apparatus of a certain efiiciency, a considerably smaller number of elements is required than has hitherto been required. H, for instance, a freely radiating element made in accordance with the present invention, is loaded with a double load, 0. g. with 4 watts, instead of with two, only half of the radiating surface in comparison with the old art, is required, which means a corresponding considerable decrease of the construction material which serves as a covering for the stoves, and, consequently, a considerable reduction of the manufacturing cost of stoves of the same efficiency.

In the following I have described, in connection with the accompanying drawings, one form of device illustrating my invention, the features thereof being more fully set forth hereinafter in the claims.

In the drawings Fi ure 1 is a plan view and Fig. 2 a section a ong the line AB in he resistance, as shown, is made of a strip of metal 0, which is painted on the mica strip a and then fired. On the outside, the strip 0 is covered by the mica strip b. The two mica strips aand b are surrounded by sheet metal d for nearly their entire lengths. The sheet metal (1 extends only a short distance over the sides of the strip 1) aslshown in the drawings. Between the two bent over side edges of the sheet metal piece d, a flat piece of sheet metal 9 is inserted substantially covering the mica strip 12, and a layer of asbestos e placed over the metal strip. The metal sheet g might be placed between resistance 0 and mica strip 6 and the asbestos strip e placed directly over the mica strip b but I prefer the arrangement of parts first described. Two U-shaped pieces of thick sheet metal f are placed over the said parts in such a manner that they nearly touch each other on their longitudinal edges, '5. e. they embrace the said parts like clamps. The sheet metal pieces f bear, as soon as they are subjected to a pressure of about 350 kg. per square centemeter, perfectly firmly against the parts inclosed by them and form with them a single whole. With the strip of resistance 0 are electrically connected the caps or conductors 7t adapted to conduct the current to the resistance. One or the other of the two pieces of sheet metal covering f is, in certain cases, extended beyond the heating element, in order to transmit the heat to a still larger surface. The Ipieces f may in that case be provided with oles or the like, which permit the heating resistances to be easily screwed, or otherwise fastened, onto a surface.

Where heating elements are concerned in which, instead of a resistance of fine metal painted onto the mica, a wire or the like, is wound upon mica or a strip of asbestos, to be used as resistance, such a heating element, after having been inclosed in the above-described manner in the sheet metal covering, is pressed together and thus intimately connects the parts, so that such elements maybe used in the same way as those referred to. t It is obvious that the exact arrangement of parts disclosed is not material to the invention and that parts, such as the asbestos strip or the overlaying metal strip, may be omltted Without departing from the spirit of the invention.

What I claim and desire to secure by Letters Patent is 1. An apparatus for electric heating devices comprising a mica strip, a resistance layer fixed thereon, a conducting covering, a non-conductor inserted between said resistance layer and the conducting covering, and a second conducting covering composed of U-shaped pieces of like construction substantially' surrounding the aforesaid parts and pressed together upon these parts so as to form the .whole into a unitary structure.

2. An apparatus for electric heating devices comprising an insulated resistance strip, a heat conducting covering partially inclosing the same, a sheet metal strip resting on said insulated resistance between the edges of said heat conducting covering, and a second heat conducting covering substantially inclosing the aforesaid parts, the whole combined as a unitary structure by pressing the second heat conducting covering thereon.

3. An apparatus for electric heating de vices comprising an insulated resistance strip, a heat conducting covering partially inclosing the same, a sheet metal strip adjacent to the uncovered portion of said insu-..

lated resistance, an asbestos covering onEnne side of said insulating strip, and a second heat conducting covering of two like U; shaped pieces substantially inclosing the aforesaid parts and pressed down upon them to form a unitary structure.

4. An apparatus for electric heating devices comprising a mica strip, a metallic resistance fired thereon, a second mica strip substantially inclosing them and the Whole protecting said resistance, a sheet .;metal combined to form a unitary structure by strip substantially covering said last named pressing the second covering down thereon. mica strip, a sheet-Inetalcovering inclosing In testimony whereof I have hereunto 5 the first-named -mica strip and having its signed my name in the presence of two sub- 15 edges adjacent to the edges of said sheet scribing Witnesses.

metal stri an asbestos strip superimposed FRIEDRICH BQLLING on said .s eet metal strip, and a second Witnessesr 7 sheet metal covering of like U -shaped; JEAN GRUND,

0 pieces applied to these parts edgewise and l CARL GRUND. 

